RFI in the monitors

[Ben Walters]

Hi guys,

I just moved, and my new room seems to have extreme amounts of RF - both sets of monitors are picking up a radio station quite clearly. The NS10s are particularly bad, being completely unshielded. All my audio components are powered through a power conditioner, cable runs are kept to a minimum, I don't have any CRTs, and switching off all the electrical devices I can find doesn't seem to change the problem. What can I do? I can't work like this!

Ben.

[Curtis Franklin]

I have this problem as well (but not to the same degree).

Is there a way to shield the entire room? I often use my control room for guitar overdubs, and the amount of RFI is beginning to become unacceptable.

I realize that I can shield every piece of gear seperatly, but I would like to be able to use any guitar that a client brings in w/o modifying it.

Thanks

[tINY]

You are driving the active monitors witha balaced signal, aren't you?




-tINY

[Berolzheimer]

He said NS-10s- obviously not powered. Can't matter that the speakers aren't shielded, if there's strong enough RF in the air to get a speaker moving I'd think they'd be microwave coooking your internal organs too.

Must be something at instrument or line level.

[Ben Walters]

Originally Posted by tINY

You are driving the active monitors witha balaced signal, aren't you?

Yes I am. My output chain is RME D/A -> SPL 2381 Monitor controller -> musikelectronic RL 901 powered speakers OR Alesis RA-100 -> NS-10M.

The signal is balanced all the way to the power stage in both paths. In my previous location with the same cables there was no detectable noise. Unplugging the input to the power stages still lets me listen to KUOW 94.9 FM. I've tried replacing the cables between the power stages and the speakers, and the signal is coming through all four speakers so I don't think it's a defective cable.

[Ben Walters]

Thanks Doc! I'll experiment with building cable shields and let you all know how it goes.

[Berolzheimer]

[QUOTE=APOHStudios. By doing this, you are creating a balanced cable.

Doc[/QUOTE



Not really- most amplifier outputs are unbalanced, And there's certainly no common mode rejection on the input of a speaker to eliminate noise on the leads. That said, creating as sheild might prevent RF from getting into the speaker wires, but I seriously doubt there's strong enough RF in the air to generate voltages in the wires that could get a speaker moving. Plus by shielding your speaker wires you run the risk of adding capacitance to the amp/speaker circuit.Besides, he said the RF shows up in his other monitors as well, didn't he?

It might be getting into your ground plane.

[Ben Walters]

The power supply is a good suspect, but since I have all of these devices running on a UPS doesn't that decouple the ground from the grid? I was wondering the same thing about the powered speakers: they are XLR balanced inputs, so I would expect them to have a grounded shield and they do indeed pick up the signal, though at a lower level than the NS-10s.

[goobersezhey]

Same business going on here.

The culprit is my new cell phone, which makes any speaker within 15 feet beep and click. I can tell two seconds beforehand that my phone is going to ring, just by sitting near my monitors. It happens on my home stereo, too; but, it doesn't happen in the car, leading me to believe that it may, in fact, be the cabling. I just put my phone in the other room and I'm usually left in peace.

Or, by RF, did you really mean radio? You might want to complain to the FCC that you're getting said radio station on your blender and toaster and see if they'll check the transmitter for compliance.

[Ben Walters]

Originally Posted by goobersezhey

Same business going on here.

The culprit is my new cell phone, which makes any speaker within 15 feet beep and click. I can tell two seconds beforehand that my phone is going to ring, just by sitting near my monitors. It happens on my home stereo, too; but, it doesn't happen in the car, leading me to believe that it may, in fact, be the cabling. I just put my phone in the other room and I'm usually left in peace.

Or, by RF, did you really mean radio? You might want to complain to the FCC that you're getting said radio station on your blender and toaster and see if they'll check the transmitter for compliance.

I've been seeing that for the past couple years, especially with guitar amps. I always make guitarists leave their cell phones before heading in to track. What I'm experiencing now is constant pickup of an FM station.

[brianroth]

While testing for RFI, disconnect any leads from the inputs to the power amplifiers, leaving only the speaker leads between the amp and speakers. With a powered monitor, then just unplug the inputs to the boxes.

THEN wire up a shorting plug for the input to the amplifier. In the case of XLR inputs, then wire a SHORT pice of wire between pins 2 and 3. For a balanced 1/4" phone plug, a short piece of wire between tip and ring. For unbalanced 1/4" phone, short piece of wire between tip and sleeve.

(When I say "short piece of wire", I mean 0.000000000001" long <g>. OK, as short as possible..not some 6" long piece of crap hanging out the innards of the connector's shell).

Report back...

Bri

[tINY]

If the amp is quiet with the imput shorted out, you'll need to install a snubber cap (back of the input panel or where the balanced pair hits the first PCB would be a good place. Usually something on the order of 100-200pF works - just make sure that it's a good ceramic (like an X7R or an NP0) cap.




-tINY

[Berolzheimer]

Originally Posted by APOHStudios

"

"Not really- most amplifier outputs are unbalanced, And there's certainly no common mode rejection on the input of a speaker to eliminate noise on the leads."

I am aware of this. By placing a grounded shield around the monitor leads what have you done? Explain the difference, in essence, what a balanced cable is compared to what I said. Two conductors with a shield, right? Where does that shield connect to? Ground?

.

Not trying to be condescending here, Just answering- A balanced cable such as a mic cable has essentially 2 lines of defensee against noise- the shield, connected to ground, which (hopefully) will carry any rf noise to ground before it gets to the signal conductors. The second mechanism is that the signal is carried on the 2 leads identically, but polarity reversed- one of them swings upward from 0v ref'd to to ground, the other wings negative ref'd to ground- then at the input the reversed signal is reversed again and added to the non-reversd version, cancelling out any noise that has gotten into the lines, assuming that it's the same in both. This is called CMR, common mode rejection, and it's the main purpose of having balanced interconnections. So you see, just having 2 conductors and a shield doesn't make it a balanced signal.

[vintage junky]

I just bought some Truth B2031a's (they sound ok) they are my first pair of monitors so im pretty happy just to have something. My question is...... why the hell was there no RF in them when i first set them up,(there was dead silence when they were on .....i mean you couldn't here anything it was great) but when I returned from work they are so damn noisy and im frustrated , and im picking up radio lowd as @$#&. I can't focus on my music because i can hear this bullshit what can i do..... please help im new with this sort of thing... I wan't nothing more than to solve this and to learn something from this.